Well, its inexplicable to me, You can not reduce the length, if its not all to be paved the contract must be altered. For safety sake. I am not sure what shape the threshold is in but makes to sense in any context to displace and shorten, if that is what is happening. As you say if its not too bad it could be feathered into the existing work I would think. That 500' off the length is 500' off the safety margin and they usually do land long but they should not, they should be touching down in the first 500' for sure and we dont want a shorter runway. What were they thinking if at all? No pilot made that decision that is for sure.